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<meta name="description" content="作者：苏苏链接：https://www.zhihu.com/question/270343200/answer/738213054来源：知乎人在直立行走之后，肛门比心脏低了很多，那部位的静脉血液回流就不太好，而排便的压迫又会导致肛周充血。这两个原因共同作用，结果就是排便时局部快速充血，但消肿很慢。长此以往（每天重复），即使很注意个人卫生，痔疮还是会不请自来。而四肢行走的哺乳动物即使从来不擦屁股也没">
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<meta property="og:description" content="作者：苏苏链接：https://www.zhihu.com/question/270343200/answer/738213054来源：知乎人在直立行走之后，肛门比心脏低了很多，那部位的静脉血液回流就不太好，而排便的压迫又会导致肛周充血。这两个原因共同作用，结果就是排便时局部快速充血，但消肿很慢。长此以往（每天重复），即使很注意个人卫生，痔疮还是会不请自来。而四肢行走的哺乳动物即使从来不擦屁股也没">
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        <p>作者：苏苏<br>链接：<a href="https://www.zhihu.com/question/270343200/answer/738213054" target="_blank" rel="noopener">https://www.zhihu.com/question/270343200/answer/738213054</a><br>来源：知乎<br>人在直立行走之后，肛门比心脏低了很多，那部位的静脉血液回流就不太好，而排便的压迫又会导致肛周充血。这两个原因共同作用，结果就是排便时局部快速充血，但消肿很慢。长此以往（每天重复），即使很注意个人卫生，痔疮还是会不请自来。而四肢行走的哺乳动物即使从来不擦屁股也没有这种毛病，因为它们的肛门基本是和心脏保持水平的，血液回流没有压差的障碍。这个问题恐怕很难通过进化来解决，由于消化道需要足够的长度才能完成消化过程，肛门位置的提高会使消化道缩短，造成吸收效率降低，那样就需要吃流食，或者更大量的进食才能保证营养和能量的补充，从某种意义上看这不是进化，反而是退化（生存成本提高，则生存难度随之增加）。但是如果消化道整体结构不变，单单提高肛门位置，那么最末端这一段肠道必然是由下向上的，由于重力作用，会对排便造成巨大困难，所以也行不通。至少目前尚未看到身体找到了合适的进化方向来解决痔疮问题，也可能永远解决不了，痔疮将是人类永远的痛，肛肠科医生则是全人类最好的朋友。其实避免此病的方法很简单，但大多数人只在人生的最后阶段才会去做，而且还是不情愿的，那就是平躺着拉屎，拉完别急着起来，再多躺一会儿。更新：谢谢此位朋友提供的经验，也借此对我前面的结论做点调整：躺着拉不太重要，重要的是拉完了躺着。</p>

      
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